In recent years, a lithography process for manufacturing semiconductors demands a higher degree of miniaturization according to the progress of downsizing of semiconductor devices. Specifically, since microfabrication of 100 nm or less is now demanded in a lithographic process, various methods for forming fine patterns using a photoresist material responding to irradiation with rays with a short wavelength such as an ArF excimer laser, F2 excimer laser, and the like have been studied.
In such a lithography technology, because a limitation to the degree of miniaturization is unavoidable due to the restriction of wavelength of rays to which the photoresist material is exposed, researches to enable formation of detailed patterns which surpass the wavelength limit have been undertaken heretofore. Specifically, a method for miniaturizing resist patterns by a process comprising patterning a resist for electron beams such as polymethyl methacrylate, applying a positive-tone resist onto the resist pattern, treating the positive-tone resist with heat to form a reaction layer on the boundary of the resist pattern and the positive resist layer, and removing the unreacted part of the positive-tone resist (Patent Document 1), a method of forming a reaction layer between a lower layer resist pattern and an upper layer resist using heat crosslinking with an acid generator or an acid (Patent Document 2), a method for manufacturing a semiconductor device using a fine pattern-forming material comprising a water soluble resin, a water-soluble crosslinking agent, or a mixture of these dissolved in an aqueous solvent, but not containing a photosensitive component, as a solution for applying an upper layer resist (Patent Document 3), a method comprising forming a photosensitive layer of a chemically-amplified resist on a substrate, irradiating to form an image and developing to form a resist pattern, applying a coating film-forming agent comprising a water soluble resin such as polyvinyl acetal, a water-soluble crosslinking agent such as tetra(hydroxymethyl)glycoluril, a water-soluble nitrogen-containing organic compound such as amine, and, optionally, a surfactant containing fluorine and silicon to the resist pattern, heating the resultant coating film to form a water-insoluble reaction layer on the interface of the resist pattern and the coating film for miniaturizing the resist pattern, and removing the unreacted area of the coating film for miniaturizing the resist pattern with pure water (Patent Document 4), and the like have been proposed.
Although these methods are preferable due to their capability of miniaturizing patterns surpassing the wavelength limit of a photosensitive resist (under layer resist) in a simple manner by using a fine pattern-forming material (upper layer resist), they have problems such as crosslinking of the fine pattern-forming material in unnecessary areas in the bottom of the resist pattern, a skirt-like configuration, inadequate verticality of the cross-sectional configuration of the fine pattern-forming material, or an effect of mixing bake (heating causing crosslinking) on the upper layer resist pattern size and the pattern profile. Moreover, since these processes have a high heat dependency of about 10 to 20 nm/° C., and it is difficult to maintain a uniform temperature in a wafer plane during enlargement of a substrate or miniaturization of patterns, there is another problem of poor pattern-size-controlling-performance. Furthermore, a fine pattern-forming material using the above-mentioned water-soluble resin has a problem of low resistance to dry etching due to a limitation of water solubility. Low dry etching resistance leads to a problem of inaccurate transcription of a resist pattern to a substrate when a pattern is transferred to the substrate by dry etching using the resist pattern as a mask in fabricating a semiconductor device.
In addition, a heat flow process which comprises forming a photoresist pattern on a substrate, heating or radiating the pattern to fluidize the photoresist pattern, and reducing the pattern size to a size smaller than the resolution limit has been proposed (Patent Documents 5 and 6).
However, because controlling fluidity of a resist by heat or radiation is difficult in this process, it is difficult to obtain products with a constant quality. In another process developed based on the heat flow process, the fluidity of a photoresist is controlled by providing a water-soluble resin film on the substrate after forming the resist pattern (Patent Document 7). However, because the solubility and stability over time of the water-soluble resin such as polyvinyl alcohol used in this process are insufficient for removing the resin with water, a residue remains after washing with water.
In order to form a fine resist pattern by heat shrinkage of the resist pattern formed by using a photoresist, a coating agent for miniaturizing a resist pattern that can be removable by washing with water after heat shrinking of the resist pattern on which upper layer coat-forming agent is previously provided and a method for efficiently forming a fine resist pattern using that agent have been proposed (Patent Document 8). In this method, the coating agent for miniaturizing a resist pattern is an aqueous-type agent and can only insufficiently cover fine resist patterns such as contact holes with a diameter of 100 nm or less. In addition, a cup required for exclusively applying the aqueous-type agent results in a cost increase. Moreover, the coating agent has a problem of freezing or depositing at a low temperature during transportation and the like.
(Patent Document 1) Japanese Patent No. 2723260
(Patent Document 2) JP-A-6-250379
(Patent Document 3) JP-A-10-73927
(Patent Document 4) JP-A-2001-19860
(Patent Document 5) JP-A-1-307228
(Patent Document 6) JP-A-4-364021
(Patent Document 7) JP-A-7-45510
(Patent document 8) JP-A-2003-195527